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Abstract

Fast T-scanning (transverse scanning, en-face) was used to build B-scan or C-scan optical coherence tomography (OCT) images of the retina. Several unique signature patterns of en-face (coronal) are reviewed in conjunction with associated confocal images of the fundus and B-scan OCT images. Benefits in combining T-scan OCT with confocal imaging to generate pairs of OCT and confocal images similar to those generated by scanning laser ophthalmoscopy (SLO) are discussed in comparison with the spectral OCT systems. The multichannel potential of the OCT/SLO system is demonstrated with the addition of a third hardware channel which acquires and generates indocyanine green (ICG) fluorescence images. The OCT, confocal SLO and ICG fluorescence images are simultaneously presented in a two or a three screen format. A fourth channel which displays a live mix of frames of the ICG sequence superimposed on the corresponding coronal OCT slices for immediate multidimensional comparison, is also included. OSA ISP software is employed to illustrate the synergy between the simultaneously provided perspectives. This synergy promotes interpretation of information by enhancing diagnostic comparisons and facilitates internal correction of movement artifacts within C-scan and B-scan OCT images using information provided by the SLO channel.

96 4-C-scan ICG/OCT/SLO sets of a patient with polypoidal choroidal vasculopathy. (a) XY display (View 1); (b) Light-box display (View 2). The SLO image in the upper left of each 4-up C-scan appears thickened with a lumpy, multi-lobular or “polypoidal” texture to the surface of the retina, as shown by the arrows. (Counter 15 s on the ICG image): Early arterial phase of ICG sequence reveals abnormal choroidal vessels. OCT depth is within the choroid and shows evidence of shadowing. (Counter 28 s on the ICG image): Mid arterial-venous phase demonstrates a leash of deep abnormal vessels with hyper-fluorescent bulbous endings. OCT image outlines the overlying serous elevation surrounding the vessels and hot spots. (Counter over 1 minute on the ICG image): Full venous phase of the ICG angiogram shows increased leakage at vessel endings. The OCT reveals the outlines of the serous cuff around the vessels and enlarging fluorescence accumulations. In all C-scan images, lateral size is 22°×22°.

ICG/OCT/SLO sets of the same patient as that in Fig. 3 (with polypoidal choroidal neovascularization). 18 B-scan OCT images (View 3) are collected for 7 different orientations of the red line projected over the ICG image, through different areas of leakage: images 1, 2, 3, 14 and 15 (1st orientation), images 4 and 5 (2nd orientation), image 6 (3rd orientation), images 7, 8 and 9 (4th orientation), images 10, 11, 12 (5th orientation), image 13 (6th orientation) and images 16, 17 and 18 (7th orientation). The OCT reveals corrugated elevation of the RPE. The straightness and the verticality of the lines in the images provided by the SLO channel in the lower right frame confirm good alignment with minimal movement artifacts. The Z-axis (according to Fig. 1) of the B-scan (vertical Y axis in the display) is expanded by the horizontally confined configuration of the multi-channel display producing a vertical exaggeration of the aspect ratio. C-scan images: lateral size is 22°
×22°. B-scan OCT image: lateral size (horizontal) is 22° and 1.3 mm in depth (vertical, measured in air).

Wide display of B-scan images in the B-scan regime, for the same patient as that in Fig. 3 (with polypoidal choroidal neovascularization). 6 B-scan OCT images (View 4) are collected for 3 different orientations of the red line projected over the SLO image (bottom right). Images 1, 2 and 6 (1st orientation), images 3 and 4 (2nd orientation) and image 5 (3rd orientation). The inset underneath the B-scan image on the right displays the C-scan just before switching the systems from C-scan to B-scan. The SLO image in the inset underneath on the left is the image generated by the SLO channel in the B-scan regime. B-scan OCT image, lateral size 22° and 1.3 mm in depth (measured in air).

4-up image display of scans acquired in the first 1 minute from a patient with recurrent choroidal neovascularization (View 6). X-Y: Each image in the panel captures the same 29 degrees, since only one scan is actually performed with feeds to 3 separate channels. The panel seen in the lower right of the 4-up is a mixture of the ICG channel (lower left) and the C-scan OCT (upper right). The ICG sequence shows the contrast dye enters the normal vessels and the abnormal nest of choroidal neovascularization at the edge of the old laser scar.

For the same patient as in Fig. 7, illustration of the eye movement correction of the C-scan OCT images and of the ICG images using the information in the SLO channel in (a) and validation of this correction on the inferred B-scan images in (b). (a) X-Y display: by scrolling the cursor through the 36 images it can be noticed that the retina features are stable transversally, the bright lesion is fixed while the small bright patch corresponding to the interface optics stray reflection oscillates transversally (View 7); (b) X-Z (top) and Y-Z (bottom) display: traces of the retina are now vertical. Image 420 in the X-Z sequence and image 149 in the Y-Z sequence show cuts through the interface optics stray reflection. Their waved contours display the eye movement in the X-Z and in the Y-Z plane, respectively (View 8).

Comparison of B-scan inferred traces in the stacks of C-scan images in Figs. 7 and 8, illustrating the capability of detection of lateral eye movements using the SLO image, and the possibility of using such information to align transversally all the C-scan images in the 4-up display. The depth axis is oriented upwards in all images.

Panel of 4 images generated in the B-scan regime (View 9) for the same patient as that in Fig. 7 (with recurrent choroidal neovascularization). 34 images made of two C-scans (left column) and the pair of images OCT/SLO in the B-scan regime (right column), following a 1st image in the set which is a 4-up all C-scan images. The system has been switched into the B-scan regime at 1 minute 50 seconds after the ICG injection, starting with the image number 2. The B-scan OCT in the upper right panel reveals a corrugated inner retinal surface due to cicatricial contraction from the previous laser treatment. The lower left panel shows retained ICG dye in the vessels and some leakage at the site of the membrane. The spatial limitations imposed upon the aspect ratio due to the 4-up display results in compression of the horizontal dimension producing a somewhat exaggerated vertical appearance of the cross-sectional features of the B-scan. The frame in the lower right shows the lateral movements during the acquisition of the B-scan OCT. Note the lateral shifts in vertical lines.

Display of 4 images in the B-scan regime (View 11) for the same patient as that in Fig. 11 (CSR case). 7 images are shown obtained for three different positions of the red line over the ICG image in the bottom left. Image 1 (for the 1st position), images 2, 3 and 4 (2nd position) and images 5, 6 and 7 (3rd position).

The images on the left show the SLO (top) and ICG image (bottom) just before the system was switched into B-scan regime. The columns in the middle represent instances where the eye has moved laterally while collecting the B-scan image (top) as shown by the jaggedness of the vertical bright traces in the SLO image (bottom). Corrected B-scan OCT mages are shown in the next column, where the bright traces underneath show the effect of the alignment by being moved in the opposite direction. Two sets are shown (View 16), for a polypoidal choroidal vasculopathy (1st set) and for a diabetic retinopathy case (2nd set).

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